Binding of reduced antibody to Protein-A?? - (Oct/24/2011 )

I have recently observed that when antibodies (IgG1) are reduced they fail to bind to “Protein A” (from Staphylococcus aureus)?? why is this so, is the whole Fc part of the antibody needed for the binding with ‘Protein-A” ?? Doesn’t single chain “heavy-chain” bind to them??